Abstract: Cracks between the inclusion and the matrix metal are major defects affecting the forgings’ fatigue life and impact properties. In hot forging processes, the stress field around a brittle inclusion is one of the most important factors for crack coalescence. In order to study the stress field’s influence on crack initiation, the definition of average relative spherical stress(ARSS) and its mathematical expression are given. Influences of ARSSes of various stress fields on matrix metal-brittle inclusion crack growth are investigated by way of numerical simulation. Results show that existing matrix metal-brittle inclusion cracks can coalesce only when the algebraic value of the ARSS of the stress field around the inclusion is smaller than its critical value and there exists a certain amount of deformation. Hot compression test are done using dedicated specimens and anvils on a Gleeble-3180 thermo-mechanical simulator. Cracks before and after compression tests in the specimens are observed with a scanning electron microscope. Experimental results agree well with the numerical ones.

Key words: average relative spherical stress, brittle inclusions, free forging, heavy forgings, numerical simulation